The invention concerns a capacitor closure disc unit of a type comprising a metal plate encircled by a rubber sealing material.
Such capacitor closure disc usually consists of aluminum and serves to close off condenser housings which in most cases are also made of aluminum. The sealing rubber element which encircles the outer rim of the cover plate serves firstly as a gas-proof and liquid-proof seal between the plate and case housing and secondly to insulate electrically the plate from the case housing. The base of the mostly wound-up type of the capacitive unit inserted in the housing, usually has one of its terminals connected to the housing, and the other connected to the cover plate.
Such a capacitor closure disc is known from the disclosure of Swedish Published Patent Application No. 314 743. Its sealing rubber element is a prefabricated, preshaped rubber part, especially of tubular section. The diameter of the tubular section in its unstressed state is smaller than the diameter of the metallic plate. The tubular section, after being stretched radially, is placed radially around the metallic plate. The closure unit, after being prepared in this manner, is inserted into the upper rim of the housing which is then closed off in the usual manner by rolling down its rim and forming a seam. This known capacitor closure disc or condenser cover plate has the disadvantage that the metallic plate and the sealing rubber element must be manufactured separately in the form of individual parts and thus require an additional processing step for their preassembly.
Although the above-described technique for closing-off cup capacitors has been widely known for almost ten years, the sealing rubber elements for the cover plates of such capacitors are still being produced in the form of prefabricated rubber parts despite the uneconomic assembly required by such parts. This is possibly due to the fact that a flat, parallel sided aluminum disc, generally used for closing-off such housings, is not suitable for the application of a rubber ring by injection molding techniques because of technical mold difficulties. As a result, even the mere possibility of applying sealing rubber elements to flat capacitor cover plates consisting of metal by an injection molding method has been beyond the scope of closing-off techniques taken into consideration by persons skilled in the art.
It is an object of the invention in view of this present state of the art to provide a capacitor closure disc which simplifies and thus reduces the costs of the closing-off of the capacitor housing.
It is another object of the present invention to provide a novel capacitor closure unit, and method for making, which enables the sealing material to be applied by injection molding.
It is a further object of the invention to provide a novel capacitor insulated plate wherein centering of the plate in a mold is facilitated.